2004-03-31 04:00:00 PDT Washington -- A unanimous U.S. Supreme Court on Tuesday ruled that border agents have wide freedom to search vehicles entering the United States, even if they do not have a specific reason to suspect wrongdoing.

Writing for the court, Chief Justice William Rehnquist said border authorities need broad discretion to search vehicles to combat drug trafficking and terrorism.

The decision overturned a Ninth Court of Appeals ruling that such inspections violated the constitutional guarantee against unreasonable searches and seizures of evidence.

Rehnquist said searches of vehicles are "reasonable simply by virtue of the fact that they occur at the border."

"The government's interest in preventing the entry of unwanted persons and effects is at its zenith at the international border," Rehnquist said.

More than 90 million Mexican vehicles enter the United States every year, according to the U.S. Embassy in Mexico.

as he entered the Otay Mesa port of entry on the California border with Mexico.

U.S. Customs Agent Visente Garcia noticed that Flores-Montano avoided eye contact and his hand was shaking as he handed the agent his passport. Garcia said the gas tank sounded solid when he tapped it with a screwdriver, a possible indication that the tank could be filled with drugs.

Garcia told the driver to pull the car into an inspection station. A mechanic then spent an hour taking apart the vehicle's gas tank where he discovered 81 pounds of marijuana bricks.

Flores-Montano was arrested and indicted on drug-trafficking charges.

At his trial in U.S. District Court in San Diego, Flores-Montano asked the judge to suppress the evidence taken from his gas tank. He argued that the Fourth Amendment's protection against unreasonable search and seizure bars border agents from taking apart a person's car based solely on a hunch that the law has been broken.

The trial court sided with Flores-Montano, calling the search "intrusive. " The District Court said the removal of a vehicle's gas tank could not be considered routine.

During arguments in February, Theodore Olson, the administration's top lawyer, said that forcing customs inspectors to show "reasonable suspicion" before searching a vehicle would endanger the country.

"Such a decision would create an appreciable risk of encouraging terrorists to use gas tanks as a means to avoid the detection of explosives or other hazardous substances crossing the country's borders," he said.

Rehnquist rejected Flores-Montano's argument that the disassembly of his gas tank violated the Fourth Amendment, saying the expectation of privacy was less at the border than inside the country.